diff --git a/Cargo.lock b/Cargo.lock
index d67181bd5628..9d40b14f0bf1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -162,7 +162,7 @@ source = "git+https://github.com/CraneStation/cranelift.git#387593d6c94d291e614c
 dependencies = [
  "cranelift-codegen 0.46.1 (git+https://github.com/CraneStation/cranelift.git)",
  "cranelift-module 0.46.1 (git+https://github.com/CraneStation/cranelift.git)",
- "object 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "object 0.14.0 (git+https://github.com/gimli-rs/object.git)",
  "target-lexicon 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -341,7 +341,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 [[package]]
 name = "object"
 version = "0.14.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
+source = "git+https://github.com/gimli-rs/object.git#50391629ce0691dda4fb6ea57cf920cee80130c6"
 dependencies = [
  "crc32fast 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "flate2 1.0.12 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -431,7 +431,7 @@ dependencies = [
  "indexmap 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.64 (registry+https://github.com/rust-lang/crates.io-index)",
  "libloading 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "object 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "object 0.14.0 (git+https://github.com/gimli-rs/object.git)",
  "target-lexicon 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -629,7 +629,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum mach 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "86dd2487cdfea56def77b88438a2c915fb45113c5319bfe7e14306ca4cd0b0e1"
 "checksum miniz_oxide 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "304f66c19be2afa56530fa7c39796192eef38618da8d19df725ad7c6d6b2aaae"
 "checksum nodrop 0.1.14 (registry+https://github.com/rust-lang/crates.io-index)" = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
-"checksum object 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)" = "81afbc5773e99efe9533d8a539dfac37e531dcd0f4eeb41584bae03ccf76d4c2"
+"checksum object 0.14.0 (git+https://github.com/gimli-rs/object.git)" = "<none>"
 "checksum plain 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "b4596b6d070b27117e987119b4dac604f3c58cfb0b191112e24771b2faeac1a6"
 "checksum proc-macro2 0.4.30 (registry+https://github.com/rust-lang/crates.io-index)" = "cf3d2011ab5c909338f7887f4fc896d35932e29146c12c8d01da6b22a80ba759"
 "checksum proc-macro2 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)" = "90cf5f418035b98e655e9cdb225047638296b862b42411c4e45bb88d700f7fc0"
diff --git a/Cargo.toml b/Cargo.toml
index 86347a006d7d..3c2c4c8d8ec9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -45,6 +45,10 @@ features = ["compression", "read", "std"] # We don't need WASM support
 #[patch.crates-io]
 #gimli = { path = "../" }
 
+[patch.crates-io]
+# FIXME switch back to crates.io once gimli-rs/object#133 is published
+object = { git = "https://github.com/gimli-rs/object.git" }
+
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
 cranelift-simplejit = { git = "https://github.com/CraneStation/cranelift.git" }
 
@@ -52,7 +56,7 @@ cranelift-simplejit = { git = "https://github.com/CraneStation/cranelift.git" }
 # By compiling dependencies with optimizations, performing tests gets much faster.
 opt-level = 3
 
-[profile.dev.overrides."rustc_codegen_cranelift"]
+[profile.dev.package.rustc_codegen_cranelift]
 # Disabling optimizations for cg_clif itself makes compilation after a change faster.
 opt-level = 0
 
@@ -62,14 +66,14 @@ opt-level = 0
 opt-level = 0
 debug = false
 
-[profile.dev.overrides.cranelift-codegen-meta]
+[profile.dev.package.cranelift-codegen-meta]
 opt-level = 0
 debug = false
 
-[profile.dev.overrides.syn]
+[profile.dev.package.syn]
 opt-level = 0
 debug = false
 
-[profile.dev.overrides.synstructure]
+[profile.dev.package.synstructure]
 opt-level = 0
 debug = false
diff --git a/example/mini_core.rs b/example/mini_core.rs
index a271cb6e62ef..1d8942c6ab2c 100644
--- a/example/mini_core.rs
+++ b/example/mini_core.rs
@@ -1,6 +1,6 @@
 #![feature(
     no_core, lang_items, intrinsics, unboxed_closures, type_ascription, extern_types,
-    untagged_unions, decl_macro, rustc_attrs
+    untagged_unions, decl_macro, rustc_attrs, transparent_unions
 )]
 #![no_core]
 #![allow(dead_code)]
@@ -448,10 +448,17 @@ pub trait Drop {
     fn drop(&mut self);
 }
 
-#[allow(unions_with_drop_fields)]
+#[lang = "manually_drop"]
+#[repr(transparent)]
+pub struct ManuallyDrop<T: ?Sized> {
+    pub value: T,
+}
+
+#[lang = "maybe_uninit"]
+#[repr(transparent)]
 pub union MaybeUninit<T> {
     pub uninit: (),
-    pub value: T,
+    pub value: ManuallyDrop<T>,
 }
 
 pub mod intrinsics {
diff --git a/example/mini_core_hello_world.rs b/example/mini_core_hello_world.rs
index 76387e8c036b..fdc71af44374 100644
--- a/example/mini_core_hello_world.rs
+++ b/example/mini_core_hello_world.rs
@@ -196,7 +196,7 @@ fn main() {
         }
 
         unsafe fn uninitialized<T>() -> T {
-            MaybeUninit { uninit: () }.value
+            MaybeUninit { uninit: () }.value.value
         }
 
         zeroed::<(u8, u8)>();
diff --git a/patches/0017-Fix-libtest-compilation.patch b/patches/0017-Fix-libtest-compilation.patch
index b7a7267cd787..c76e2e2f8b42 100644
--- a/patches/0017-Fix-libtest-compilation.patch
+++ b/patches/0017-Fix-libtest-compilation.patch
@@ -12,18 +12,18 @@ index 8b76080..9e65de2 100644
 --- a/src/libtest/lib.rs
 +++ b/src/libtest/lib.rs
 @@ -52,7 +52,7 @@ use std::fmt;
- use std::fs::File;
- use std::io;
- use std::io::prelude::*;
--use std::panic::{self, catch_unwind, AssertUnwindSafe, PanicInfo};
-+use std::panic::{self, PanicInfo};
- use std::path::PathBuf;
- use std::process;
- use std::process::{ExitStatus, Command, Termination};
+     env,
+     io,
+     io::prelude::Write,
+-    panic::{self, catch_unwind, AssertUnwindSafe, PanicInfo},
++    panic::{self, PanicInfo},
+     process,
+     process::{Command, Termination},
+     sync::mpsc::{channel, Sender},
 @@ -1493,7 +1493,7 @@ pub fn run_test(
      fn run_test_inner(
          desc: TestDesc,
-         monitor_ch: Sender<MonitorMsg>,
+         monitor_ch: Sender<CompletedTest>,
 -        testfn: Box<dyn FnOnce() + Send>,
 +        testfn: Box<impl FnOnce() + Send + 'static>,
          opts: TestRunOpts,
@@ -65,8 +65,8 @@ index 8b76080..9e65de2 100644
      report_time: bool,
 -    testfn: Box<dyn FnOnce() + Send>,
 +    testfn: Box<impl FnOnce() + Send + 'static>,
-     monitor_ch: Sender<MonitorMsg>,
-     time_opts: Option<TestTimeOptions>,
+     monitor_ch: Sender<CompletedTest>,
+     time_opts: Option<time::TestTimeOptions>,
  ) {
      // Buffer for capturing standard I/O
      let data = Arc::new(Mutex::new(Vec::new()));
@@ -75,12 +75,12 @@ index 8b76080..9e65de2 100644
          None
      };
 -    let result = catch_unwind(AssertUnwindSafe(testfn));
-+    let result = Ok::<(), Box<dyn Any + Send>>(testfn());
++    let result = Ok::<(), Box<dyn std::any::Any + Send>>(testfn());
      let exec_time = start.map(|start| {
          let duration = start.elapsed();
          TestExecTime(duration)
 @@ -1688,10 +1676,10 @@ fn spawn_test_subprocess(desc: TestDesc, report_time: bool, monitor_ch: Sender<M
-     monitor_ch.send((desc.clone(), result, exec_time, test_output)).unwrap();
+     monitor_ch.send(message).unwrap();
  }
  
  fn run_test_in_spawned_subprocess(
diff --git a/prepare.sh b/prepare.sh
index 6795558422ff..2d9d1d9f908b 100755
--- a/prepare.sh
+++ b/prepare.sh
@@ -1,7 +1,7 @@
 #!/bin/bash --verbose
 set -e
 
-rustup component add rust-src
+rustup component add rust-src rustc-dev
 ./build_sysroot/prepare_sysroot_src.sh
 cargo install hyperfine || echo "Skipping hyperfine install"
 
diff --git a/src/backend.rs b/src/backend.rs
index ccb95624badf..305248182b5c 100644
--- a/src/backend.rs
+++ b/src/backend.rs
@@ -1,4 +1,5 @@
 use std::collections::HashMap;
+use std::convert::TryFrom;
 
 use rustc::session::Session;
 
@@ -122,8 +123,13 @@ impl WriteDebugInfo for ObjectProduct {
         id: SectionId,
         data: Vec<u8>,
     ) -> (object::write::SectionId, object::write::SymbolId) {
+        let name = if self.object.format() == target_lexicon::BinaryFormat::Macho {
+            id.name().replace('.', "__") // machO expects __debug_info instead of .debug_info
+        } else {
+            id.name().to_string()
+        }.into_bytes();
+
         let segment = self.object.segment_name(StandardSegment::Debug).to_vec();
-        let name = id.name().as_bytes().to_vec();
         let section_id = self.object.add_section(segment, name, SectionKind::Debug);
         self.object.section_mut(section_id).set_data(data, 1);
         let symbol_id = self.object.section_symbol(section_id);
@@ -137,10 +143,13 @@ impl WriteDebugInfo for ObjectProduct {
         from: &Self::SectionId,
         reloc: &DebugReloc,
     ) {
-        let symbol = match reloc.name {
-            DebugRelocName::Section(id) => section_map.get(&id).unwrap().1,
+        let (symbol, symbol_offset) = match reloc.name {
+            DebugRelocName::Section(id) => {
+                (section_map.get(&id).unwrap().1, 0)
+            }
             DebugRelocName::Symbol(id) => {
-                self.function_symbol(*symbol_map.get_index(id).unwrap().0)
+                let symbol_id = self.function_symbol(*symbol_map.get_index(id).unwrap().0);
+                self.object.symbol_section_and_offset(symbol_id).expect("Debug reloc for undef sym???")
             }
         };
         self.object.add_relocation(from.0, Relocation {
@@ -149,7 +158,7 @@ impl WriteDebugInfo for ObjectProduct {
             kind: RelocationKind::Absolute,
             encoding: RelocationEncoding::Generic,
             size: reloc.size * 8,
-            addend: reloc.addend,
+            addend: i64::try_from(symbol_offset).unwrap() + reloc.addend,
         }).unwrap();
     }
 }
diff --git a/src/common.rs b/src/common.rs
index ff38c71fde9c..c3563dc0533f 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -286,7 +286,9 @@ pub struct FunctionCx<'clif, 'tcx, B: Backend + 'static> {
     pub clif_comments: crate::pretty_clif::CommentWriter,
     pub constants_cx: &'clif mut crate::constant::ConstantCx,
     pub caches: &'clif mut Caches<'tcx>,
-    pub source_info_set: indexmap::IndexSet<SourceInfo>,
+
+    // FIXME switch back to `SourceInfo`, once it derives `Eq` and `Hash` again.
+    pub source_info_set: indexmap::IndexSet<(Span, mir::SourceScope)>,
 }
 
 impl<'tcx, B: Backend> LayoutOf for FunctionCx<'_, 'tcx, B> {
@@ -365,7 +367,7 @@ impl<'tcx, B: Backend + 'static> FunctionCx<'_, 'tcx, B> {
     }
 
     pub fn set_debug_loc(&mut self, source_info: mir::SourceInfo) {
-        let (index, _) = self.source_info_set.insert_full(source_info);
+        let (index, _) = self.source_info_set.insert_full((source_info.span, source_info.scope));
         self.bcx.set_srcloc(SourceLoc::new(index as u32));
     }
 }
diff --git a/src/debuginfo.rs b/src/debuginfo.rs
index 762fa8668bfb..e6d133c64510 100644
--- a/src/debuginfo.rs
+++ b/src/debuginfo.rs
@@ -252,7 +252,7 @@ impl<'a, 'tcx> FunctionDebugContext<'a, 'tcx> {
         tcx: TyCtxt,
         context: &Context,
         isa: &dyn cranelift::codegen::isa::TargetIsa,
-        source_info_set: &indexmap::IndexSet<SourceInfo>,
+        source_info_set: &indexmap::IndexSet<(Span, mir::SourceScope)>,
     ) {
         let line_program = &mut self.debug_context.dwarf.unit.line_program;
 
@@ -292,7 +292,7 @@ impl<'a, 'tcx> FunctionDebugContext<'a, 'tcx> {
                 line_program.row().address_offset = offset as u64;
                 if !srcloc.is_default() {
                     let source_info = *source_info_set.get_index(srcloc.bits() as usize).unwrap();
-                    create_row_for_span(line_program, source_info.span);
+                    create_row_for_span(line_program, source_info.0);
                 } else {
                     create_row_for_span(line_program, self.mir_span);
                 }
diff --git a/src/driver.rs b/src/driver.rs
index 215ae071c3f6..22271460b02b 100644
--- a/src/driver.rs
+++ b/src/driver.rs
@@ -184,10 +184,7 @@ fn run_aot(
 
     let mut module = new_module("some_file".to_string());
 
-    let mut debug = if tcx.sess.opts.debuginfo != DebugInfo::None
-        // macOS debuginfo doesn't work yet (see #303)
-        && !tcx.sess.target.target.options.is_like_osx
-    {
+    let mut debug = if tcx.sess.opts.debuginfo != DebugInfo::None {
         let debug = DebugContext::new(
             tcx,
             module.target_config().pointer_type().bytes() as u8,